Research work performed in this laboratory in last few years was directed to the study of renal tubular transport mechanism of amino acids, sugars and electrolytes. We have shown there is a structural specificity in renal tubular transport for such compounds. We propose to pursue our work in answering the following questions: (1) Where is the carrier transport system for these amino acid located? (2) Is the renal reabsorptive process of the amino acid sodium-dependent, as we have found in the intestinal transport of amino acids? (3) What is the mechanism of intestinal transport of electrolytes under various environmental conditions? It is our intention to use the microperfusion technique to perfuse a surface proximal tubule and the microinfusion technique to infuse a peritubular capillary to determine the actual rate of secretion and actual rate of tubular reabsorption of the test amino acid. Subsequently, we will study the effect of heavy metals on tubular transport and to determine the primary target site of action. The second part of our proposed work is to utilize the Ussing chamber technique in studying the intestinal transport of electrolytes and the mechanism of adaptation under various environmental conditions.